(Reuters) - U.S. Representative Martha McSally, a former Air Force combat pilot, said on Friday she would run against former sheriff Joe Arpaio, a close ally of President Donald Trump, in the race for the Republican nomination for a key Senate seat from Arizona.

FILE PHOTO - U.S. Representative Martha McSally (R-AZ), flanked by Senator John Cornyn (R-TX) and Senator Dick Durbin (D-IL), speaks as U.S. President Donald Trump holds a bipartisan meeting with legislators on immigration reform at the White House in Washington, U.S. January 9, 2018. REUTERS/Jonathan Ernst

The August primary contest is shaping up as the latest election to expose the divisions roiling the Republican Party, pitting the establishment-backed McSally against the bomb-throwing Arpaio.

McSally, 51, and Arpaio, 85, are expected to try to capture the insurgent appeal of Trump, a popular figure among Arizona Republicans. Both are seeking to succeed Republican Senator Jeff Flake, who announced he would not seek re-election after emerging as a leading critic of Trump within the president’s own party.

Arpaio, who entered the race on Tuesday, was pardoned by Trump last year after being convicted of criminal contempt of court for refusing to obey a court order in a racial profiling case focusing on Hispanics targeted as potential illegal immigrants.

In announcing her bid, McSally told Washington Republicans in a YouTube video to “grow a set of ovaries” and said that she, like Trump, is tired of “PC politicians with their BS excuses,” referring to political correctness.

“After taking on terrorists in combat, the liberals in the Senate won’t scare me one bit,” McSally said in the video released hours before she piloted herself to campaign events across the state in a World War Two-era plane.

McSally is widely seen as the national party’s preferred nominee, much as incumbent Senator Luther Strange was backed by the party’s establishment wing in the battle for the Republican nomination in a Senate special election in Alabama against hard-line evangelical Christian conservative Roy Moore.

Moore won the nomination but lost the December election to Democrat Doug Jones after being accused of sexual misconduct with girls as young as 14, costing the Republicans a Senate seat.

Political observers in Arizona said the more moderate McSally stands a far better chance of beating a Democrat in the November general election than Arpaio, the former Maricopa County sheriff known for harsh anti-immigration views. Arpaio was defeated for re-election as sheriff by a Democrat in 2016.

The winner of the Republican primary will likely face U.S. Representative Kyrsten Sinema, the Democratic front-runner. Democrats need to pick up two seats this November to wrest control of the U.S. Senate from the Republicans. Races in Arizona and Nevada are seen as their best opportunities.

Also running in the Republican primary is conservative state Senator Kelli Ward, like Arpaio a strong Trump supporter. Ward unsuccessfully challenged incumbent Arizona Senator John McCain in 2016.

Several Republican political consultants said Arpaio’s prolific fundraising and strong name recognition could marginalize Ward’s campaign, which has targeted the same bloc of Trump voters.

“She really has no place to raise money anymore,” said Chuck Coughlin, a Republican consultant in Phoenix.

DELICATE BALANCE

McSally, first elected to the House of Representatives in 2014, must strike a delicate balance between embracing Trump and appealing to more moderate voters, Republican strategists said. Trump has not endorsed a candidate in the race.

“The Arpaio entrance is going to pose a real conundrum for congresswoman McSally,” said Stan Barnes, an Arizona Republican operative. “How much daylight is she going to put between herself and the president?”

The Arizona Democratic Party highlighted what spokesman Drew Anderson called a “long, brutal and expensive” Republican civil war. Ward’s campaign has called McSally “Jeff Flake 2.0” and noted that McSally refused to endorse Trump last year.

McSally could benefit if Arpaio and Ward split the hard-line conservative vote.

“It kind of eases her path to the nomination,” said Jennifer Duffy, who analyzes Senate races for the Cook Political Report in Washington. “She can sort of let Arpaio and Ward fight it out for conservatives, and she comes across as conservative but pretty reasonable.”

Coughlin said Arpaio has a good shot, noting he boasts a loyal core of supporters and has never lost a Republican primary.

“Martha’s got a very good story to tell: A-10 fighter pilot, a female pilot in combat, trying to get immigration reform done,” Coughlin said. “But how do you get that narrative out there in the cacophony that Joe creates when he talks?”

Reporting by Joseph Ax in New York; Additional reporting by Blake Brittain in Washington and David Schwartz in Phoenix; Editing by Colleen Jenkins and Will Dunham